If $2a + 9b + 6c = -6$ and $3x + 8y + 9z = -2$, what is $-24x - 8a - 36b - 64y - 72z - 24c$ ?
Answer: $= -8a - 36b - 24c - 24x - 64y - 72z$ $= (-4) \cdot (2a + 9b + 6c) + (-8) \cdot (3x + 8y + 9z)$ $= (-4) \cdot (-6) + (-8) \cdot (-2)$ $= 24 + 16$ $= 40$